Fused loop filamentous material

ABSTRACT

A fused loop of an elongated material, such as a surgical suture, and apparatus for making the loop. Portions of one or more segments to be joined together are fused in a welding process to form a welded joint. The shear area of the fused portion of the joint determines the strength of the joint and is thus preferably relatively large. Various configurations for the welding apparatus facilitate the creation of relatively large fused portions of the joint by maximizing contact between at least one of the welding members of the apparatus and at least one of the segments to be joined.

FIELD OF THE INVENTION

The invention relates to improvements in sutures and suturing techniques, and more particularly to materials and devices for making high-strength fused suture loops during surgical procedures.

BACKGROUND OF THE INVENTION

In surgical procedures, a monofilamentous suture is typically used to stitch or secure the edges of tissue together to maintain them in proximity until healing is substantially completed. The suture is generally directed through the portions of the tissue to be joined and formed into a single loop or stitch, which is then knotted or otherwise secured in order to maintain the wound edges in the appropriate relationship to each other for healing to occur. In this manner a series of stitches of substantially uniform tension can be made in tissue. Because the stitches are individual and separate, the removal of one stitch does not require removal of them all or cause the remaining stitches to loosen. However, each individual stitch requires an individual knot or some other stitch-closing device for securing the stitch around the wound.

It is sometimes necessary or desirable to close a wound site with sutures without having to form knots or incorporate loop-closing devices in the sutures, such as, for example, in surgical repair of delicate organs or tissues, where the repair site is relatively small or restricted. A fused suture loop must provide the appropriate tension on the wound edges and the appropriate strength to maintain the wound edges in sufficient proximity for a sufficient time to allow healing to occur.

Polymer sutures are particularly amenable to various fusing or joining processes, such as, for example, welding, whereby sections of the sutures can be fused together upon application of sufficient heat to the sections to cause partial melting and fusion of the sections. Because the direct application of heat to sutures in situ may produce undesirable heating of the surrounding tissue, it is preferred to apply non-thermal energy to the suture material in situ to induce localized heating of the suture material in the areas or sections to be fused. In particular, ultrasonic energy may be effectively applied to sections of suture materials to induce frictional heating of the sections in order to fuse or weld them together.

While sutures typically fail under tensile loads applied along the principal axis of the suture, suture welds often fail in shear, i.e., in the plane of the fused region between the overlapped segments of suture material. It is desirable to have the failure strength of the suture joint be at least as great as the failure strength of the suture material away from the joint.

U.S. Pat. No. 5,417,700 to Egan and U.S. Pat. No. 3,515,848 to Winston et al. disclose apparatus and methods for ultrasonic welding of sutures. The Winston et al. patent discloses, for example, the application of mechanical energy to a segment of material to be joined in either of two different directions. For joining plastic suture materials, mechanical energy is applied in a direction substantially parallel to the axes of the segments to be joined. For joining metallic suture materials, mechanical energy is applied in a direction substantially normal to these axes. The Winston et al. patent further discloses the use of a spherical welding tip for use in joining metallic suture materials.

Although ultrasonic welding of sutures is known, it has heretofore been difficult or impossible to control the suture welding process in order to produce suture welds of sufficient strength and reliability to replace, or enhance the strength of, suture knots or other loop closure devices.

It is therefore an object of the present invention to overcome the disadvantages inherent in prior art suture loop joints and joining processes.

SUMMARY OF THE INVENTION

The present invention provides a fused loop of an elongated material, such as a polymeric or monofilamentous suture material, which has a strength in the joint region which is at least equal to, if not greater than, the strength of the parent material. The present invention also provides means for controlling the size and shape of the fused portion of the joint region in order to maximize joint strength.

According to one aspect of the invention, there is provided a fused loop of an elongated material comprising one or more segments of the material which extends along a principal axis. Portions of the segments are joined together to form a loop at a joint region which extends between first and second ends. The joint region includes a first portion of elongated material extending from the first end, a second portion of elongated material extending from the second end, and a fused portion or layer between and joining the first and second portions at points between the first and second ends of the joint region. The fused portion preferably comprises a relatively thin layer of fused material from the first and second portions.

The term "fused", as used herein, refers to material which has been heated to a plastic or fluid state and subsequently allowed to cool, so that the relatively highly-oriented molecular structure of the parent material is transformed into a relatively randomly-oriented molecular structure characterizing the fused portion of the joint region. The term "shear area", as used herein, refers to the area of the fused portion between and substantially parallel to the segments of material joined in the joint region. In contrast, the cross-sectional area of the segments or the fused portion refers to the area in a plane substantially transverse to the principal axes of the segments.

The elongated material in the first and second portions of the joint region is characterized by a relatively high degree of molecular orientation in the direction of the principal axis of the material, and thus relatively high strength in the direction of the principal axis. The fused material in the fused portion of the joint region is characterized by a relatively random molecular orientation, and thus relatively low strength in the direction of the principal axis of the material. The cross-sectional area of the first and second portions of the segment at the first and second ends of the joint region, yet outside of (i.e., not abutting) the fused portion, is greater than the cross-sectional area of the first and second portions of the joint region which abut the fused portion.

In one embodiment, the cross-sectional area of the first and second portions of the segment at the first and second ends of the joint region, yet outside of the fused portion, is approximately equal to the cross-sectional area of a segment of the elongated material outside of the joint region.

In a preferred embodiment, the total cross-sectional area of the first and second portions of the joint region which abut the fused portion is a minimum at approximately the midpoint of the fused portion. In a more preferred embodiment, the total cross-sectional area of the first and second portions of the segment at the midpoint of the fused portion is approximately half the total cross-sectional area of the first and second portions at the first and second ends of the joint region and outside of, or not abutting, the fused portion. In an especially preferred embodiment, the change in cross-sectional area of the first and second portions of the segment, per unit length of those portions, is substantially constant over the length of the fused portion of the joint region.

The elongated material may comprise a substantially monofilamentous material, such as, for example, a polymer. In a preferred embodiment, the elongated material is a thermoplastic polymer, such as a surgical suture material.

The segments of elongated material are preferably joined in a weld at the joint region. The weld can be effected with various types of energy, such as, for example, ultrasonic, laser, electrical arc discharge, and thermal energy.

The loop of elongated material can be made by joining portions of a single segment of the elongated material. Alternatively, the loop can be made by joining portions of multiple segments of the material.

The elongated material itself can comprise a single strand of a substantially monofilamentous material. Alternatively, the elongated material can comprise multiple strands of a substantially monofilamentous material which can be twisted, braided or otherwise interlinked.

Upon application of a tensile force to the joint region in the direction of the principal axis of the material, the first and second portions of the joint region are loaded substantially in tension, and the fused portion of the joint region is loaded substantially in shear. In a preferred embodiment, the following equation,

    A.sub.w τ.sub.fw =A.sub.u σ.sub.fu,

is substantially satisfied. A_(w) is the shear area of the fused portion, τ_(fw) is the shear stress to failure of the fused portion, A_(u) is the total cross-sectional area of the first and second portions near the first and second ends of the joint region and outside of (not abutting) the fused portion, and σ_(fu) is the tensile stress to failure of the first and second portions near the first and second ends and outside of (not abutting) the fused portion.

According to another aspect of the invention, there is provided an improvement to ultrasonic welding apparatus. The apparatus typically includes a first member having a first surface, a second member having a second surface, and means for moving the first member relative to the second member to define a gap between them. The first member is capable of vibrating and delivering mechanical energy at ultrasonic frequencies. The second member is stationary relative to the first member. A fixture element is adapted to receive and maintain two or more segments of a material to be welded in a predetermined alignment in the gap between the first and second surfaces of the first and second members during a welding operation. The contour of at least the first surface substantially corresponds to the contour of a segment of the material to be welded so as to promote acoustic coupling therebetween and establish substantially continuous contact between the first surface and the segment over the length of the first surface.

In one embodiment, one of the first and second surfaces is substantially convex and the other of the surfaces is substantially concave. In another embodiment, one of the first and second surfaces is substantially convex or substantially concave, and the other of the surfaces is substantially flat. In yet another embodiment, both of the first and second surfaces are substantially convex. In still another embodiment, both of the surfaces are substantially flat.

In another embodiment, the second member comprises a plurality of coupling portions which couple together to form the second surface during a welding process and separate after completion of the welding process to release the loop.

These and other features of the invention will be more fully appreciated with reference to the following detailed description which is to be read in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by the following description and figures, in which:

FIG. 1 is a perspective view of a fused loop of an elongated material;

FIG. 2A is an axial view of the fused loop of FIG. 1;

FIG. 2B is an axial view of several fused loops formed by joining multiple segments of material together;

FIG. 2C is a simplified perspective view of a multiple-stranded segment of elongated material;

FIG. 3 is a cross-sectional view of the joint region of the fused loop of FIG. 2A, taken along section lines A--A;

FIG. 4 is a cross-sectional view of the joint region of the fused loop of FIG. 2A, taken along section lines B--B;

FIG. 5 is a cross-sectional view of an end of the joint region of the fused loop of FIG. 2A, taken along section lines C--C;

FIG. 6 is a cross-sectional view of a segment of elongated material in the fused loop of FIG. 2A, taken along section lines D--D;

FIG. 7A is a side elevational view of a joint region of a fused loop made by ultrasonic welding;

FIG. 7B is a series of sectional views of a portion of the joint region of the loop shown in FIG. 7A;

FIG. 8A is a side elevational view of a joint region of a different type of fused loop made by laser welding or controlled coupling ultrasonic welding;

FIG. 8B is a series of sectional views of a portion of the joint region of the loop shown in FIG. 8A;

FIG. 9A is an axial view of a fused loop loaded in tension, in which the strength of the joint region exceeds the tensile failure strength of the elongated material;

FIG. 9B is an axial view of a fused loop loaded in tension, in which the strength of the joint region is less than the tensile failure strength of the elongated material;

FIGS. 10A, 11A, 12A, 13A and 14A are exploded perspective views of ultrasonic welding members of various geometries, and segments of material to be welded in the gaps between their respective surfaces;

FIGS. 10B, 11B, 12B, 13B and 14B are exploded side elevational views corresponding to the views of FIGS. 10A, 11A, 12A, 13A and 14A;

FIGS. 15A, 16 and 17A are side elevational views of ultrasonic welding members of various geometries engaged about a pair of segments of material to be welded;

FIG. 15B is a simplified side elevational view of the second welding member of FIG. 15A, uncoupled to show means for releasing the welded loop from the welding apparatus;

FIG. 17B is a side elevational view of the second welding member of FIG. 17A, uncoupled to show means for releasing the welded loop from the welding apparatus;

FIG. 18 is an exploded perspective view of a segment of an elongated material with its ends aligned within an ultrasonic welding apparatus designed to produce a contoured lap weld;

FIG. 19A is an axial view of the segments of material within the ultrasonic welding apparatus of FIG. 18, prior to welding; and

FIG. 19B is an axial view of the segments of material within the ultrasonic welding apparatus of FIG. 18, immediately after the welding process and prior to release of the loop.

Like elements in the respective FIGURES have the same reference numbers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a fused loop of an elongated material, such as a surgical suture. The loop has at least comparable strength to knotted loops or loops closed by other means by virtue of the properties of the fused portion of the joint region of the loop, as detailed more fully below.

As shown in FIG. 1, the fused loop 10 of the present invention comprises one or more segments 12 of an elongated material, such as a surgical suture material or other substantially monofilamentous material, which is amenable to bonding through the application of heat or energy thereto. Suitable materials for the elongated material include polymers, especially thermoplastic materials such as, for example, nylon (polyamide), polypropylene, Dacron® (polyester), polyglycolic acid (PGA), polyglyconate, and polydioxanone.

The fused loop of the present invention is preferably formed through a welding process, in which segments of the material to be joined are locally heated through the application of energy thereto until the segments fuse together. Various types of welded joints can be formed by the application of, for example, ultrasonic, thermal, laser, electrical arc discharge, or thermal energy to the segments, which can be joined, for example, in an overlapped joint.

FIG. 2A is an axial view of the fused loop shown in FIG. 1. The segment 12 of elongated material extends along a principal axis X of the material, which can be straight or curved. One or more segments 12 of the material are typically formed into a loop by, for example, overlapping portions of the respective ends 12A, 12B of the segment, as shown in FIGS. 1 and 2A, to form a joint region 14. Alternatively, as shown in FIG. 2B, both terminal and nonterminal portions of the segments of the material can be overlapped to form several fused loops joined in a single joint region 14.

The segments may already be knotted in preparation for fusion by welding, or they may simply be overlapped.

The elongated material can be made of a single strand of a substantially monofilamentous material, or it can comprise multiple strands, as indicated in FIG. 2C. The multi-stranded material can be twisted, braided or otherwise interlinked to increase the density, and thus the strength, of the composite strand.

The joint region 14 extends between first and second ends 14A, 14B and includes a first portion 16 of elongated material extending from the first end 14A, and a second portion 18 extending from the second end 14B. The joint region 14 further includes a fused portion 20 which has a substantially uniform thickness and which is disposed between the first portion 16 and second portion 18 of the joint region. The fused portion 20 is made of material from the first and second portions 16, 18 which has been fused together. In a preferred embodiment, all of the fused material is disposed within a fused layer or portion 20. However, some of the melted and fused material may form outside of the fused portion 20 as a result of forces applied to the segments 16, 18 to compress them together during the welding process.

As mentioned previously, the elongated material of the type used in surgical sutures is substantially monofilamentous, and preferably polymeric. Because the molecular structure of monofilamentous materials is highly oriented along the principal axis of the material, the material exhibits relatively high strength in the direction of its principal axis. The elongated material in the loop segment outside the joint region 14, as well as in the first and second portions 16, 18 of the joint region, is characterized by a relatively high degree of molecular orientation in the direction of the principal axis X of the material. As a consequence of this highly oriented molecular structure, the strength of the elongated material outside the joint region, and in the first and second portions 16, 18 of the joint region, is also relatively great in the direction of the principal axis X. On the other hand, the material which makes up the fused portion 20 of the joint region 14 is characterized by a relatively random molecular orientation, by virtue of its having been heated locally to a plastic state by the application of energy, such as ultrasonic energy, to the segment portions 16, 18 which make up the joint region 14. As a consequence of this relatively nonoriented molecular structure, the strength of the material in the fused portion 20 of the joint region is relatively low in the direction of the principal axis.

The shear area of the fused portion 20 is approximately defined as the product of the length L and the width W of the fused portion 20, as shown in FIG. 4. As will be detailed more fully below, for maximum joint strength, it is desirable to have a relatively large shear area of the fused portion 20 of the joint region.

FIG. 6 indicates the cross-sectional area of a typical segment of elongated material outside the joint region. Although the elongated material can be a strand or filament having a substantially circular cross-section, the invention is not limited to such geometries and can include elongated materials having elongated or other cross-sectional geometries, such as, for example, relatively flat ribbons having elliptical or rectangular cross-sections, or others. FIG. 5 indicates the cross-sectional area of the elongated material at the ends of the joint region, outside of the fused portion 20. As can be seen in FIGS. 3, 7 and 8, the total cross-sectional area of the portions 16, 18 abutting the fused portion 20 of the joint region 14 is somewhat less than the total cross-sectional area of the first and second portions 16, 18 in the joint region but outside of, and not abutting, the fused portion 20. As is clearly shown in FIGS. 2A and 3, some of the elongated material in portions 16 and 18 of the joint region is transformed during the welding process from an elongated, relatively highly oriented material, to a fused, relatively randomly-oriented material in the fused portion 20. Compression of the portions 16, 18 during the welding process ensures that the fused portion 20 has a relatively large shear area and a relatively small thickness.

The change in cross-sectional area of the overlapping segments 16, 18 in the joint region is preferably uniform and gradual over the length of the fused portion 20. FIGS. 7A, 7B, 8A and 8B illustrate the change in cross-sectional area of the overlapping segments of elongated material in the joint region 14 throughout the length of the fused portion 20 for different types of welded joints. At the ends 14A, 14B of the joint region, outside of or beyond the fused portion 20, the cross-sectional area of the segment portions 16, 18 is a maximum value, as the segment portions have not been caused to deform plastically at these points. As the cross-hatched areas 21a-21e in the joint region 14 indicate in FIG. 7B, the cross-sectional area of each of the overlapped segment portions 16, 18 decreases gradually from a maximum value at the ends of the fused portion 20 to a minimum value at or near the midpoint of the fused portion. Preferably, at the midpoint of the fused portion 20, the total cross-sectional area of the segments 16, 18 not sacrificed to form the fused portion is approximately half the total cross-sectional area of the segments 16, 18 at the first and second ends 14A, 14B of the joint region and beyond, or outside of, the fused portion 20.

The lap welded joint shown in FIG. 8A is characterized by a continuously varying cross-sectional area of the segments 16 and 18 in the region of the fused portion 20. As indicated in FIG. 8B, the cross-sectional area 21a-21e of one segment 16 continuously decreases from a maximum value at end 14B to a minimum value at the opposite end 14A, whereas the cross-sectional area of the other segment 18 continuously increases from a minimum value at end 14B to a maximum value at the opposite end 14A. At approximately the midpoint of the fused portion 20, the cross-sectional areas of the segment portions 16, 18 are approximately equal and are preferably equal to about half the total cross-sectional areas of the segment portions 16, 18 at the first and second ends 14A, 14B of the joint region and outside the fused portion 20.

Other geometries of the first and second portions 16, 18 in the joint region 14 which provide a uniform change in cross-sectional area of the joined segments in the joint region are also considered to be within the scope of the invention.

In a preferred embodiment of the invention, the shear area of the fused portion 20 of the joint region is sufficiently large to ensure that the joint will not fail prematurely, i.e., before the parent elongated material fails. The joint preferably has a failure strength of approximately the strength of the parent material. Most preferably, the joint has a failure strength in shear which is approximately equal to the failure strength in tension of the parent material.

Upon application of a tensile force to the joint region 14 in the direction of the principal axis X of the material, the first and second portions 16, 18 of the joint region are loaded substantially in tension and the fused portion 20 of the joint region is loaded substantially in shear. In this situation, the following equation,

    A.sub.w τ.sub.fw =A.sub.u σ.sub.fu,

is substantially satisfied, wherein A_(w) is the shear area of the fused portion 20 (i.e., the area of the layer of the fused portion which is between the first and second portions 16, 18, not the cross-sectional area of this layer), τ_(fw) is the shear stress to failure of the fused portion, A_(u) is the total cross-sectional area of the first and second portions 16, 18 near the first and second ends of the joint region 14, outside of and not abutting the fused portion, and σ_(u) is the tensile stress to failure of the first and second portions near the first and second ends, outside of and not abutting the fused portion.

If the above equation is not satisfied, the strength of the fused portion 20 may be either stronger or weaker than the strength of the parent elongated material. It is of course preferred that the fused portion 20 be at least as strong as the unfused parent material. If it is stronger, when the joint is loaded in tension, as indicated by force arrows F in FIGS. 9A and 9B, the material will fail in tensile mode, and the loop will break at a point which is outside the fused portion, and possibly outside the joint region, as indicated in FIG. 9A. If the fused portion 20 is weaker than the parent material, the fused material within the joint will fail in shear mode, and the loop will separate at the fused portion, as indicated in FIG. 9B.

FIGS. 10A-14B illustrate various geometries for ultrasonic welding apparatus, and more particularly for the vibratory and stationary members of an ultrasonic welding tip, which includes a first member 30 and a second member 32. The first member 30 is capable of vibrating and delivering mechanical energy at ultrasonic frequencies, as is known in the art. The first member 30 is movable relative to the second member 32, so that a gap or space can be defined between the first and second members. The gap is sufficiently large to accommodate two or more segments 16, 18 of material to be joined together. The ultrasonic welding apparatus further includes fixture means for aligning and maintaining the segments 16, 18 in a predetermined alignment and orientation during the welding process.

The first and second members 30, 32 each have respective surfaces 30A, 32A which are contoured to promote acoustic coupling between the first member 30 and the segment 16 of material to be joined, and to provide substantially continuous contact between at least the first surface 30A and at least one of the segments to be welded. The size of the shear area of the fused portion 20, and thus the strength of the joint region, is determined by the length and width of the surfaces 30A, 32A, the extent of contact between these surfaces and the segments 16, 18, and particularly between the first surface 30A and the segment 16 closest to the first surface, and the pressure exerted on the segments by the first member 30 in the direction of arrow 35 during welding.

In addition to the geometries of the surfaces of the first and second members, the geometry of the material to be joined must be considered. Fused portions having the largest shear areas and the greatest joint strengths can be obtained by configuring the surface 30A of the first member 30 to have a contour which corresponds to the contour of the material to be joined so as to ensure maximum contact with the segment portion 16. For example, if the material is a filament having a substantially circular cross-section, the surface 30A should have a rounded contour to match the contour of the filament in contact with it. If the material is a substantially flat ribbon, the surface 30A should be substantially flat to ensure maximum contact with the segment. If the material has a polygonal or elliptical cross-section, the contour of the surface 30A should be grooved or channeled or otherwise shaped to correspond as closely as possible to the geometry of the cross-section of the material.

It is generally preferred to configure the ultrasonic welding tip members 30, 32 so that their respective surfaces 30A, 32A engage the segment portions 16, 18 so as to provide a maximum shear area for the fused portion 20. Various geometries for the surfaces 30A, 32A are illustrated in FIGS. 10A-14B.

As shown in FIGS. 10A and 10B, the surface 30A of the first member 30 is concave about the z and x axes, whereas the surface 32A of the second member 32 is convex about the z axis. The illustrated segments 16, 18 have a circular cross-section but need not be limited to a particular geometry. Contact between the first surface 30A and the top segment 16 is substantially continuous over the entire length and width of the surface 30A as a result of the contour of that surface. The shear area of the resulting fused portion 20 is relatively large, and thus the strength of the fused portion can be expected to be relatively high.

An advantage of incorporating a convex curvature to the second surface 32A is that the length of the joint region 14 in the direction of the principal axis of the material can be reduced, thereby decreasing the diameter of the resulting fused loop of suture material.

The surfaces 30A, 32A of the embodiment illustrated in FIGS. 14A and 14B have the same relationship to each other as in the embodiment of FIGS. 10A and 10B. The resulting fused portion 20 is relatively large, with relatively high strength.

As shown in FIGS. 15A, 16 and 17A, the first surface 30A of the first member 30 can have a channeled or grooved geometry to increase the extent of contact between the first surface 30A and the segment 16. As also indicated in FIGS. 15B, 16 and 17B, the second member 32 may be comprised of multiple parts which act to confine and maintain the alignment of the segments 16, 18 during the welding process. The coupling portions of the second member separate after the welding process to release the joined material from the confines of the welding apparatus without requiring the loop to be moved or otherwise manipulated. FIGS. 15A, 15B and 16A illustrate one type of ultrasonic welding apparatus, in which the second member 32 couples together beneath the segments of material joined at the joint region. The coupled members remain engaged during the welding process, as shown in FIGS. 15A and 16A, and separate after the welding process by a hinging or pivoting action to release the loop, as shown in FIG. 15B.

FIGS. 17A and 17B illustrate another type of apparatus, in which the multiple parts of the second member 32 slide away from each other to release the joined loop. Other configurations for the second member 32 which permit the loop to be released after the welding operation is completed are considered to be within the scope of the invention.

FIGS. 18, 19A and 19B illustrate still another configuration for the welding apparatus, in which the segment portions 16, 18 to be welded are confined and aligned or oriented relative to each other within the walls of the second member 32. This apparatus produces welded joints having a fused portion 20 in a vertical orientation instead of a horizontal orientation. In this apparatus, the first member 30 is complementary with and fits inside two sections of the second member 32, which extend vertically on either side of the first member. The surfaces 30A, 32A of the first and second members are substantially flat, although they can be cambered and contoured otherwise, as previously discussed. As shown in FIG. 19A, the overlapping portions 16, 18 of segment 12 of material to be joined together are oriented in a vertically diagonal alignment within the multiple parts of the second member 32. During the welding process ultrasonic energy is delivered from a power supply and converted to mechanical energy to establish local frictional heating between the segment portions 16, 18. Pressure is exerted on the segment portions 16, 18 in the direction of arrow 35 as the segments are heated to a plastic state, causing portions of the segments to flow and to fuse in a vertically oriented fused portion 20. Because the first and second members 30, 32 are configured to confine and maintain the alignment of the overlapping segments during the welding process, the joint region 14 and fused portion 20 are relatively dense and compact, with little, if any, fused material disposed in regions outside of the fused portion 20. It is desirable to minimize the extrusion of fused material beyond the fused portion 20 so as to maximize the strength of the loop joint region and to avoid irritation of the surrounding tissue.

As in the above embodiments, the coupling portions of the second member 32 can be separated after the welding process to release the joined loop.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of the equivalency of the claims are therefore intended to be embraced therein. 

What is claimed is:
 1. A fused loop of an elongated material, comprising:one or more segments of said material extending along a principal axis, portions of said segments being oppositely directed and joined together to form a loop at a joint region extending between first and second ends and including:i. a first portion of elongated material extending from said first end, ii. a second portion of elongated material extending from said second end, and iii. a fused portion between said first and second portions, said fused portion comprising a relatively thin layer of fused material from the first and second portions, wherein the elongated material in said first and second portions of the joint region is characterized by a high degree of molecular orientation in the direction of the principal axis of the material and high strength in the direction of the principal axis relative to the degree of molecular orientation and strength in other than the direction of the principal axis, and the fused material in the fused portion of the joint region is characterized by a low degree of molecular orientation in the direction of the principal axis of the material relative to the degree of molecular orientation in other than the direction of the principal axis, and the first and second portions at the first and second ends of the joint region outside of the fused portion have cross-sectional areas which are greater than the cross-sectional areas of the first and second portions of the joint region which abut the fused portion.
 2. A fused loop of an elongated material according to claim 1, wherein the cross-sectional area of the first and second portions at the first and second ends of the joint region and outside of the fused portion is approximately equal to the cross-sectional area of a segment of the elongated material outside of the joint region.
 3. A fused loop of an elongated material according to claim 2, wherein the cross-sectional areas of said first and second portions of the joint region abutting the fused portion are a minimum at approximately the middle of the fused portion.
 4. A fused loop of an elongated material according to claim 3, wherein the cross-sectional areas of said first and second portions at approximately the middle of the fused portion are approximately half the cross-sectional areas of the first and second portions at the first and second ends of the joint region and outside of the fused portion.
 5. A fused loop of an elongated material according to claim 4, wherein a change in the cross-sectional areas of the first and second portions per unit length of the first and second portions in the direction of the principal axis of the elongated material is substantially constant over the length of the fused portion.
 6. A fused loop of an elongated material according to claim 5, wherein said elongated material comprises a substantially monofilamentous material.
 7. A fused loop of an elongated material according to claim 6, wherein said monofilamentous material is a polymeric material.
 8. A fused loop of an elongated material according to claim 7, wherein said monofilamentous material is a thermoplastic material.
 9. A fused loop of an elongated material according to claim 8, wherein said monofilamentous material comprises a surgical suture material.
 10. A fused loop of an elongated material according to claim 5, wherein said oppositely directed segments of said material are joined together in a lap weld at said joint region.
 11. A fused loop of an elongated material according to claim 10, wherein said weld is effected using ultrasonic energy.
 12. A fused loop of an elongated material according to claim 10, wherein said weld is effected using laser energy.
 13. A fused loop of an elongated material according to claim 10, wherein said weld is effected using electrical arc discharge energy.
 14. A fused loop of an elongated material according to claim 10, wherein said weld is effected using thermal energy.
 15. A fused loop of an elongated material according to claim 5, wherein said loop is defined by joining oppositely directed portions of a single segment of said material.
 16. A fused loop of an elongated material according to claim 5, wherein said loop is defined by joining oppositely directed portions of a plurality of segments of said material.
 17. A fused loop of an elongated material according to claim 5, wherein upon application of a tensile force to said joint region in the direction of the principal axis of the material so that the first and second portions of said joint region are loaded substantially in tension and the fused portion of said joint region is loaded substantially in shear, the following equation is substantially satisfied:

    A.sub.w τ.sub.fw ≧A.sub.u σ.sub.fu,

wherein A_(w) is the shear area of the fused portion, τ_(fw) is the shear stress to failure of the fused portion, A_(u) is the sum of the cross-sectional areas of the first and second portions of the joint region near the first and second ends of the joint region and outside of the fused portion, and σ_(fu) is the tensile stress to failure of the first and second portions of the joint region near the first and second ends of the joint region and outside of the fused portion.
 18. A fused loop of an elongated material according to claim 6, wherein said segment of said elongated material comprises a single strand of said substantially monofilamentous material.
 19. A fused loop of an elongated material according to claim 6, wherein said segment of said elongated material comprises a plurality of strands of said substantially monofilamentous material.
 20. A loop formed of elongate surgical suture material extending along a principal axis, in which oppositely directed end portions of said material are overlapped and joined together by fusion and compression in a joint region, such that the joined material in the joint region has a low degree of molecular orientation relative to the degree of molecular orientation of material outside of said joint region, and the overlapped material in the joint region retains a high degree of molecular orientation in the direction of the principal axis of the material relative to the degree of molecular orientation of material in other than the direction of the principal axis, wherein the cross-sectional areas of the overlapped material and of the joined material both gradually change over the length of the joint region.
 21. A loop according to claim 20, wherein the cross-sectional area of the overlapped material is greater at the ends of the joint region and smaller at the middle of the joint region, and wherein the cross-sectional area of the joined material is greater at the middle of the joint region and smaller at the ends of the joint region. 